1. Field of the Invention
The present invention relates to a musical tone forming apparatus which is employed by an electronic musical instrument and the like.
2. Prior Art
In an example of the musical tone forming apparatus which is employed by the electronic musical instrument, a waveform memory is provided to store musical-tone-waveform data representing instantaneous values of a musical tone waveform, from its start portion to its end portion, of an acoustic sound which is produced by an acoustic musical instrument (i.e., non-electronic musical instrument); and then, the stored data are read out to form a musical tone signal. However, a large storage capacity should be required for the waveform memory to store all of the musical-tone-waveform data with respect to each tone color, each tone pitch and each register. Therefore, if a semiconductor memory is used for the waveform memory, there is a problem that the cost for manufacturing the apparatus should be raised up. Thus, it can be proposed that instead of using the semiconductor memory, a magnetic disk unit is used for the waveform memory. Because, the magnetic disk unit has a large storage capacity and the price thereof is relatively inexpensive. However, when using the magnetic disk unit, there occurs another problem that the production of the musical tone cannot be performed simultaneously with the depression of the key of the keyboard, because the read-out speed of the magnetic disk unit is not so high.
Under the consideration of the above-mentioned problems, some apparatus as disclosed in Japanese Patent Publication No. 64-1800 is proposed. This apparatus is characterized by providing two kinds of storage units. Herein, a first storage unit is made by the semiconductor memory which is exclusively used for the read-out operations and whose read-out speed is relatively high, while a second storage unit is made by the magnetic disk unit, and the like, whose storage capacity is relatively large. The first storage unit stores a part of musical-tone-waveform data relating to an attack portion of the musical tone waveform, wherein the attack portion corresponds to a certain period of time "T" from the rise time of the musical-tone waveform. The second storage unit stores another part of musical-tone-waveform data relating to a remaining portion of the musical tone waveform other than the attack portion.
In another apparatus as disclosed in Japanese Patent Laid-Open Publication No. 61-22398, both of the first and second storage units are made by the magnetic disk unit. Herein, the storage area of the first storage unit is divided into a plurality of sectors, each of which stores the musical-tone-waveform data relating to the attack portion of the musical tone waveform such that the data stored in one sector overlaps with the data stored in another sector. According to this apparatus, when the key is depressed, the musical-tone data relating to the attack portion of the musical tone waveform corresponding to the depressed key is read from the first storage unit, so that a first musical tone signal corresponding to the attack portion of the musical tone waveform is generated at first. During the generation of the first musical tone signal, the second storage unit is accessed, so that the musical-tone-waveform data relating to the remaining portion of the musical tone waveform other than the attack portion is read-out. After a certain period of time "T" is passed, a second musical tone signal corresponding to the above-mentioned remaining portion of the musical tone waveform is generated. Herein, a selector is provided to alternatively output either the data read from the first storage unit and the data read from the second storage unit. The above-mentioned configuration of the apparatus is advantageous in that a delay in the production of the musical tone can be eliminated; therefore, it is possible to instantaneously start the reproduction of the musical tone waveform stored in the magnetic disk unit externally provided.
In the known musical tone forming apparatus as described above, it is necessary to reproduce the musical tone waveform without causing any discontinuous points. In order to do so, just after the first musical tone signal is outputted, the second musical tone signal should be simultaneously outputted. As described before, the first musical tone signal relates to the attack portion of the musical tone waveform and is generated by the data read from the first storage unit, while the second musical tone signal relates to the remaining portion of the musical tone waveform and is generated by the data read from the second storage unit. For this reason, a buffer memory is conventionally provided between the second storage unit and the selector, for example. The buffer memory can be configured by a first-in-first-out memory (i.e., FIFO memory). Since the buffer memory temporarily stores an output signal of the second storage unit, it is possible to adjust output timings of the data respectively read from the first and second storage units. Thus, the musical tone forming apparatus conventionally known must have a complex configuration. In addition, the conventional apparatus requires the circuits for connecting the two storage units, so that the size of the apparatus must be enlarged. In fact, the musical tone forming apparatus conventionally known suffer from those problems.